1. Field of Invention
The invention relates to a cooling structure of a fan motor which is used, for example, as an automotive electric part.
2. Description of Related Art
In general, a fan motor of the kind mentioned above is disposed in an engine compartment and is arranged to cool an engine. Because the fan motor runs at high power, it is necessary that the motor have a forced intake of external air (cooling air) into the interior of the motor so as to enhance heat dissipation inside the motor. To this end, for example, a fan motor cooling structure has been proposed in JP-A-9-74718, wherein a motor yoke has a cooling air intake port provided at a lower portion of an open end thereof. Alternatively, JP-A-8-340654 discloses a cooling structure in which a cooling air inlet is formed in an upper portion of an end case which is provided at its one side with brush holders, and an end frame having an air vent hole formed in a lower portion thereof is provided on the other side of the end case, wherein cooling air drawn through the air vent hole is introduced into an annular space formed between the end frame and the peripheral surface of a bearing portion of the end case. The cooling air is then introduced into the motor via the cooling air inlet.
In the first-mentioned known structure, the cooling air intake port is formed on the lower portion of the interior of the motor, and cooling air is led to the interior of the motor by way of a labyrinth structure having a relatively short air flow path from the cooling air intake port. Therefore, although this arrangement is superior in cooling performance, the arrangement is inferior in waterproofing and dust-proofing the motor.
On the other hand, in the second-mentioned known cooling structure, external cooling air is introduced into the gap between the end frame and the end case through the air vent hole positioned at the lower portion of the end frame, and the introduced cooling air is led to the interior of the motor through the cooling air inlet located at the upper portion of the end case. Therefore, the cooling air is introduced into the interior of the motor through a spiraling passage so as to swirl around the bearing unit, along a comparatively long labyrinth structure. That is, the arrangement according to the latter publication provides a labyrinth having a relatively long air flow path. Accordingly, although the arrangement is superior in waterproofing and dust-proofing characteristics, the arrangement is inferior in air flow and cooling performance because cooling air is introduced into a restricted path that extends from a single intake port at the lower portion of the end frame upward via the annular gap. Further, as the end frame and the brush holders constitute part of a labyrinth structure within the motor assembly, the structure of the motor is complicated and bulky. Thus, both of the above arrangements suffer from a cumbersome structure and cannot simultaneously achieve superior cooling performance and superior waterproof and dust-proof performance.
The invention seeks to solve the problems described above.
According to one aspect of the invention, there is provided a cooling structure of a fan motor, including a cylindrical case which is open at one end and is closed by an end closure at the other end in a longitudinal direction, the end closure having air exhaust ports; an end case which closes the open end of the cylindrical case, the end case having at least one air passage hole; a cover member disposed in the vicinity of the end case so as to cover the air passage hole; and ring-shaped ribs disposed between the cover member and the end case so as to form a labyrinth structure; whereby air is set to flow into the periphery of the cover member, inside the cylindrical case through the labyrinth structure and through the air passage hole, and to be discharged through the exhaust ports of the cylindrical case.
With this arrangement, it is possible to simultaneously achieve high cooling performance as well as superior waterproof and dust-proof characteristics within the motor.
The arrangement may be such that the end case is provided at its side adjacent to the cylindrical case with brush holders and a bearing holder for holding a bearing to support an armature shaft of the fan motor, the end case being recessed towards the cylindrical case so as to provide an annular recess in which the at least one air passage hole is formed, and wherein the ring-shaped ribs including a first ring-shaped rib and a second ring-shaped rib are provided on the cover members, the first ring-shaped rib loosely fitting over the outer periphery of the open end of the cylindrical case and the second ring-shaped rib adjacently opposing the inner peripheral surface of the annular recess on the outer diametrical side, whereby the cooled air is set to flow into the outer periphery of the cover member, inside between the cover member and the end case, and through the labyrinth structure made up of the first and second ring-shaped ribs, the open end of the cylindrical case and the annular recess, then from the air passage hole into inside the cylindrical case and then to be is discharged through the exhaust ports. With this arrangement better cooling performance can be achieved.
The first ring-shaped rib has a cutout for positively taking in the cooled air, resulting in providing an improved cooling performance. Preferably, an air guide plate is formed on the cutout of the first ring-shaped rib so as to guide the cooled air towards the cutout.
The arrangement may be such that the cover member is fixed to a fan shroud to which the fan motor is attached. This arrangement makes it possible to complete the cooling structure simply by mounting the fan motor on the fan shroud. Preferably, the air passage hole formed in the ring-shaped recess of the end case is defined by an axially elongated tubular guide wall which cooperates with the second ring-shaped rib in forming therebetween a part of the labyrinth structure. With the arrangement better waterproof and dustproof performance can be achieved. The end case is made of a resin material and has the brush holders and the bearing holder formed therein.
The above and other objects, features and advantages of the invention will become clear from the following description when the same is read in conjunction with the accompanying drawings.